wishlist: offer options for smaller data bundles

[mlc]

Because of moment/moment-timezone#697, the timezone data upon which js-joda-timezone relies has grown massively in size recently, and therefore so has js-joda-timezone itself.

version	dist/js-joda-timezone.min.js	gzip -9
2.0.1	186973 bytes	25331 bytes
2.0.2	931347 bytes	36084 bytes

moment-timezone is now offering builds of the package with some of the data removed if it is not relevant for timestamps within ±5 years or so of the present. It would be good if js-joda-timzeone could copy this and offer smaller builds of the package for use cases where this makes sense.

[pithu]

Because we are using the tz data files from moment-timezone it shouldn't be so difficult to use the minimized versions. We are open for PR.

[jkillian]

Hey @mlc I ran in to the same issue as you, so I put up a PR, #73, to offer some alternative builds! Feel free to give it a look and comment if you ahve any thoughts